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From: jhu
Subject: an Escher-like image
Date: 24 Jan 2008 19:25:00
Message: <web.47992c10a9821a767bcf5ca50@news.povray.org>
There's still some problems with the render, such as those strange black
splotches  on the table adjacent to the clear sphere


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From: nemesis
Subject: Re: an Escher-like image
Date: 24 Jan 2008 20:00:00
Message: <web.479933ea38a94e692a13953c0@news.povray.org>
a truly excellent and imaginative Escher-inspired image, I say!

as for the blotches, perhaps something related to photons and low
max_trace_level?

the image itself is truly fantastic! And you get more points for doing it with
actual models rather than resorting to HDRI... :D


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From: jhu
Subject: Re: an Escher-like image
Date: 24 Jan 2008 20:05:00
Message: <web.4799359438a94e697bcf5ca50@news.povray.org>
Thanks! My global settings are listed below. What do you suggest I change?

global_settings {
    max_trace_level 30
    ambient_light rgb <1,1,1>
    radiosity {
      pretrace_start 0.08
      pretrace_end   0.01
      always_sample 0
      //save_file "radiosity_data.inc"

      //count 20
      count 1000

      nearest_count 10
      error_bound 0.05
      recursion_limit 5

      low_error_factor 0.2
      gray_threshold 0.4
      minimum_reuse 0.010
      brightness 1
      max_sample -1
      normal off

      adc_bailout 0.01/2
    }
  }


"nemesis" <nam### [at] gmailcom> wrote:
> a truly excellent and imaginative Escher-inspired image, I say!
>
> as for the blotches, perhaps something related to photons and low
> max_trace_level?
>
> the image itself is truly fantastic! And you get more points for doing it with
> actual models rather than resorting to HDRI... :D


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From: William Tracy
Subject: Re: an Escher-like image
Date: 24 Jan 2008 22:21:04
Message: <479955a0$1@news.povray.org>
jhu wrote:
> There's still some problems with the render, such as those strange black
> splotches  on the table adjacent to the clear sphere

Oddly enough, those splotches could pass for part of the wood texture.

I like this image. :-)

-- 
William Tracy
afi### [at] gmailcom -- wtr### [at] calpolyedu

You know you've been raytracing too long when your wife walks into the
room wearing only a smile and you start thinking of Colefax's fur macro.
    -- Ken Tyler


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From: nemesis
Subject: Re: an Escher-like image
Date: 24 Jan 2008 22:24:02
Message: <47995652$1@news.povray.org>
jhu escreveu:
> Thanks! My global settings are listed below. What do you suggest I change?

hmm, no photons for caustics?  It seems radiosity is creating some weird 
kind of caustics by its own, except it's black!

Now, count 1000 and error_bound .05?!  whew!  Took a few days to render, 
huh? ;)

In my radiosity scenes I like more fine-grained radiosity shading so I 
generally go for pretrace_start 0.04 and pretrace_end 0.008 or something 
like that.  But I go with error_bound .2:  it's acceptably slow and 
gives good results for the blending of blotches, specially coupled with 
nearest_count of about 16.  Count is about right, though I first try 
with lower counts, like 200 to 600...

As for the dark spots, the correct way to get caustics in povray is with 
photons.  Radiosity has problems with black spots and glass surfaces. 
Use a first radiosity pass without the reflective or transparent 
surfaces, save that rca file and then render the final image with 
photons and the reflective/transparent surfaces back.  Test without 
photon first, then good luck. :)


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From: jhu
Subject: Re: an Escher-like image
Date: 24 Jan 2008 23:45:00
Message: <web.4799686138a94e697bcf5ca50@news.povray.org>
OK, thanks. Never played around with photons before. I'll give it a shot. BTW,
it's "only" a 16 hour render at those settings...

nemesis <nam### [at] gmailcom> wrote:
> jhu escreveu:
> > Thanks! My global settings are listed below. What do you suggest I change?
>
> hmm, no photons for caustics?  It seems radiosity is creating some weird
> kind of caustics by its own, except it's black!
>
> Now, count 1000 and error_bound .05?!  whew!  Took a few days to render,
> huh? ;)
>
> In my radiosity scenes I like more fine-grained radiosity shading so I
> generally go for pretrace_start 0.04 and pretrace_end 0.008 or something
> like that.  But I go with error_bound .2:  it's acceptably slow and
> gives good results for the blending of blotches, specially coupled with
> nearest_count of about 16.  Count is about right, though I first try
> with lower counts, like 200 to 600...
>
> As for the dark spots, the correct way to get caustics in povray is with
> photons.  Radiosity has problems with black spots and glass surfaces.
> Use a first radiosity pass without the reflective or transparent
> surfaces, save that rca file and then render the final image with
> photons and the reflective/transparent surfaces back.  Test without
> photon first, then good luck. :)


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From: Tim Attwood
Subject: Re: an Escher-like image
Date: 25 Jan 2008 05:18:04
Message: <4799b75c$1@news.povray.org>
Did you use sky_sphere? Radiosity doesn't
play well with infinite distance backgrounds,
it can cause dark spots. Use an inverted sphere
for the sky...


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From: Stephen
Subject: Re: an Escher-like image
Date: 25 Jan 2008 05:30:42
Message: <dhejp3pqh6k54fopu8u0q9at6sqm43jquh@4ax.com>
On Thu, 24 Jan 2008 19:23:44 EST, "jhu" <nomail@nomail> wrote:

>There's still some problems with the render, such as those strange black
>splotches  on the table adjacent to the clear sphere

I do like this very much. The level of detail is very good, I am sure that I can
see texture on her sweater. Is she the sort of person who holds a mug and puts
her fingers through the handle? 
I' getting lost in this :)

And I love self referral in anything.
Excellent!


Regards
	Stephen


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From: Bill Pragnell
Subject: Re: an Escher-like image
Date: 25 Jan 2008 06:45:00
Message: <web.4799cab838a94e69731f01d10@news.povray.org>
Very nice, I always like a good Escher tribute. Looks very real. Good wood
texture! It's also quite dark but this works well.

If you solve the blotchiness (looks like radiosity artifacts to me) and
re-render it, then you might also consider using a longer camera angle to
prevent the outer spheres being stretched by perspective (if this means putting
it outside the room then the no_image keyword might come in handy). Just a
thought!

keep it up
Bill


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From: Jan Dvorak
Subject: Re: an Escher-like image
Date: 25 Jan 2008 08:08:36
Message: <4799df54@news.povray.org>
Tim Attwood napsal(a):
> Did you use sky_sphere? Radiosity doesn't
> play well with infinite distance backgrounds,
> it can cause dark spots. Use an inverted sphere
> for the sky...
> 
> 
Does it? I'll try it, thanks!


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